Q: What does Adinatha mean?

A: The Sanskrit word Adinatha means 'Primordial Lord'. It is
one of many subsects of the heterodox Natha tradition.

The Adinath Sampradaya is a tantrik sect of yogis affiliated with
the greater Natha tradition founded by Gorakhnath and Matsyendranath.
These two individuals are revered by Tibetan Lamaism as Mahasiddhas
(great magicians) and credited with great powers. 

According to George Feuerstein's Textbook of Yoga (ISBN009-124030),
"The natha siddhas...deserve to be singled out for separate
treatment by virtue of their enormous influence on the development
of yoga...the nathas have gone their own ways and evolved
many new, original theories and yogic techniques. These are
embodied in Hathayoga, also called hatha vidya or the 'science
of force' which is a direct continuation of the kaya sadhana
of the earlier siddhas."

The Nathas are connected with an earlier alchemical tradition
known as Rasayana and with the Siddhas and the Kapalikas. 
However, two figures stand out in the history of the Nathas,
Matsyendranath and Gorakhnath.